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Causes, Definitions and Explanations of Breast Cancer

In women, the breasts are made up of milk-producing glands (lobules), milk ducts, and connective tissue (stroma). Milk is produced by cells in the lobules and moves through the mammary ducts and finally to the nipple. Most breast cancers originate in mammary ducts.

 Blood and lymphatic vessels are found within the stroma surrounding the lobules and ducts:

  • Blood vessels are part of the circulatory system. They supply oxygen and nutrients to and remove waste from breast cells.
  • Lymphatic vessels are part of a large network termed the lymphatic system. These vessels collect and carry fluid and cells from the tissues of the body. Smaller lymphatic vessels merge with larger ones, as streams merge into a river. Large vessels empty into grape-like clusters of lymphatic tissue called lymph nodes. The lymphatic vessels in the breast carry lymphatic fluid to a mass of lymph nodes located near the underarm.

What Is Breast Cancer?
Breast cancer is a type of cancer that occurs when cells in the breast tissue divide and grow without control. About 80 percent of cases of breast cancer originate in the mammary ducts, while about 20 percent arise in the lobules. Cancerous tumors in the breast usually grow very slowly so by the time one is large enough to be felt as a lump, it may have been growing for as much as ten years. One of the most important distinctions to understand is between invasive breast cancer and carcinoma in situ (kar-sin-O-ma in SY-too). Below is a brief overview of the key concepts.

Invasive Breast Cancer
When abnormal cells from inside the lobules or ducts break out into the surrounding tissue, the condition is called invasive breast cancer. This term, though, does not necessarily mean that the disease may have spread beyond the breast. When invasive cancer is at its most treatable, such as when a tumor is relatively small and has not spread to the lymph nodes, it is considered "early stage." When the condition is more serious and successful treatment is less likely, such as when a tumor is very large or has spread to other organs (like the liver, lungs, and bones), it is considered "advanced stage.

Carcinoma In Situ
When abnormal cells grow inside the lobules or milk ducts but there is no sign that the cells have spread out to the surrounding tissue or beyond, the condition is called carcinoma in situ. The term "in situ," which means "in place," is used because with carcinoma in situ, the abnormal cells remain "in place" inside the lobules or ducts where they first developed. There are two main categories of carcinoma in situ: ductal carcinoma in situ and lobular carcinoma in situ.

Ductal Carcinoma In Situ (DCIS)
Normally the mammary ducts are hollow so that fluid can pass through them. With DCIS, excess cells that are very similar to invasive cancer cells grow inside the ducts. DCIS is not invasive cancer, but is considered a precancerous condition that has the potential to develop into invasive cancer eventually.

Lobular Carcinoma In Situ (LCIS)
Like the milk ducts, the lobules of the breast tissue have open space inside them. When large numbers of abnormal cells grow in the lobules, the condition is called LCIS. LCIS is not invasive cancer, and it is not a direct cancer precursor, that is, the abnormal cells found inside the lobules will not turn into cancer later on. LCIS is, however, a risk factor for invasive cancer. And, as with other risk factors for the disease, women who have LCIS are more likely to develop invasive cancer in either breast. Increasingly, providers refer to LCIS as "lobular neoplasia in situ," believing this title to be a more accurate depiction of the condition.

Breast cancer diagnosis and staging